Field of the Invention
The present invention generally relates to an image pickup apparatus and, in particular, to technology for removing a foreign substance deposited on a surface of an optical member disposed along an imaging light axis.
Description of the Related Art
Image pickup apparatuses, such as digital cameras, that capture an image by converting an image signal into an electrical signal receive light using an image pickup element, such as a charged coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) sensor. The image pickup apparatuses convert a photoelectrically converted signal output from the image pickup element to image data. Thereafter, the image pickup apparatuses store the image data on a recording medium, such as a memory card. In such image pickup apparatuses, an optical lowpass filter and an infrared cut filter are disposed on the front side (an object side) of the image pickup element.
If a foreign substance, such as dust or dirt, is deposited on surfaces of the cover glass of the image pickup element or these filters, the foreign substance generates a black spot in a captured image, and therefore, the quality of the image deteriorates.
In particular, since digital single-lens reflex cameras with interchangeable lenses include a mechanical operating unit, such as a shutter and a quick-return mirror, disposed in the vicinity of an image pickup element, a foreign substance, such as dust or dirt, is possibly generated by the operating unit and is deposited on the surfaces of the cover glass of the image pickup element and the filters. In addition, when the lens is changed, a foreign substance may enter inside the camera body from the opening of a lens mount and may be deposited on the surfaces of the cover glass of the image pickup element and the filters.
Japanese Patent Laid-Open No. 2003-319222 (corresponding to U.S. Pat. 2003-202114 A1) describes technology in which a dust-proof member that allows an imaging light beam to pass therethrough is disposed on the object side of an image pickup element and is vibrated by means of a piezoelectric element, and therefore, a foreign substance deposited on the surface of the dust-proof member is removed.
In such a structure in which a foreign substance deposited on the surface of an optical member can be removed by vibrating the optical member, a biasing force may be applied to the optical member by means of a biasing member in addition to vibrating the optical member by means of the piezoelectric element.
In Japanese Patent Laid-Open No. 2003-319222, in order to remove a foreign substance deposited on the surface of the dust-proof member, a voltage is applied to a piezoelectric element coupled with the dust-proof member so as to drive the piezoelectric element. Thus, the dust-proof member is displaced in the light axis direction so as to produce membrane oscillation.
However, in this case, a special member, that is, the dust-proof member needs to be disposed on the imaging light axis. Therefore, the layout of the members is restricted. In addition, the optical functionality and optical performance, such as the transmittance for an imaging light beam, disadvantageously deteriorate.